The genetic code is a triplet code.A sequence of 3 bases codes for one amino-acid.There are four bases in DNA (A, C, T and G). The four bases can be arranged in 64(43) different triplets. Since there are only 20 different amino acids used in proteins each amino acid has more than one triplet code so the code is said to be degenerate.A triplet is always read in one direction and is non-overlapping.The genetic code is (almost) universal. It is the same in all living organisms with a few exceptions.Three of the triplets are stop codons and mark the end of a gene.The start triplet is always ATG which codes for methionine.Genes may contain a length of non-coding sequences called introns that are removed to leave the exons or coding-sequences which are then joined together into one continuous strand before the peptide is synthesised.
The Genetic Code
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Specification: AQA Biology (7401), AS-level, 3.4.1 DNA, genes and chromosomes. Topic: DNA, Genes and Protein Synthesis.
Key terms in this lesson
- gene
- A length of DNA that codes for a polypeptide or a functional RNA molecule, at a specific locus on a chromosome.
- codon
- A sequence of three bases on mRNA that codes for a specific amino acid or a stop signal.
More in DNA, Genes and Protein Synthesis
- Genes
- Features of the Genetic Code
- Chromosomes
- Homologous Chromosomes
- Alleles
- The Human Karyotype
- Protein Synthesis
- RNA
All 15 lessons in DNA, Genes and Protein Synthesis · All AQA AS-level Biology topics